I just left the Texas region and can vouch for what Todd said. I only got to do one PCA event (which was the important one at COTA), and can say that the 944 crowd is very friendly and welcoming. Texas has been trying to get going for a while with a few split between NASA and PCA, but I think with Todd doing some coordinating with everyone, that split will disappear and most cars will show up at the same events.
On one hand its nice that NASA and PCA share rules, but in some cases when the events conflict, it can split car counts. NASA has contingency programs but PCA tends to be a bit more professionally run, IMO.
SE30 is non-existent in Texas which leaves Spec Miata and 944 Spec for the smaller momentum class spec classes. I went with 944 because I didnt feel like competing with the $12K pro motors and $70K pro car builds of Miata.
I would do 944 Spec all over again if I had the chance to start over. Another buddy of mine from college decided to go the CMC route about the same time I started. I cant count how many DNFs he's had and general work hes had to do in between races to keep going. In the 2 years of owning my car, Ive only had 1 DNF due to the cam bolt backing out. Most all of my other maintenance has been preventive in nature (oil, brakes) or typical little things that happen on all cars (radiator).
Lastly, BUY A CAR THATS ALREADY BUILT AND HAS A LOG BOOK!!! The car has already been sorted and you could be racing the week after you buy it.